Transfer cells and lipid droplets of some Valerianaceae

Development, structure and the axial distribution of transfer cells and their lignification were investigated in Valerianella locusta, Valeriana officinalis, and V. tuberosa (Valerianaceae). Fundamental new results are: (1) Transfer cells often contain numerous lipid droplets. Within the stem the distribution of cells containing lipid droplets correlates to that of transfer cells. (2) In Valeriana officinalis persisting protuberances are frequently found on pit membranes of xylem transfer cells. Lignified transfer cells can undergo a second modification: a layer covering the secondary wall forms wall ingrowths similar to those of transfer cells. (3) Peripheral pith cells, abuting transfer cells, are able to modify into transfer cells. Cambial derivatives are only temporarily developed as transfer cells. (4) Phloem transfer cells are found in vascular bundles of the whole axis. (5) In roots, xylem transfer cells are poorly developed or absent. (6) Oil cells with oil bodies are present in the rape of Valeriana tuberosa. They are absent however in the stem of the species investigated. (7) Tannins occur in elements of the primary cortex, phloem and secondary xylem of Valeriana officinalis.